Please try uninstalling with the uninstaller located in Applications/Utilities/Adobe Installers. If you have the same problem again then please try downloading and installing the trial of Photoshop CS6. Once the trial is installed you can choose the License This Software option and enter the Adobe ID tied to your Creative Cloud account.

Close and re-open PS CS6 and then check if you get that option or not. If not, goto Help Menu and check is Deactivate option is greyed out or not. If it's not greyed out, it means your PS CS6 is activated. No need to worry.

The problem began for me once I removed photoshop because the update kept failing. So I uninstalled photoshop cs6 using their uninstall script, and then re-installed it with the creative cloud application manager. From then on I could not "double click" on a .PSD to open photoshop directly, but "open with" would work. Very strange.. but the above command fixed it.